Generally, due to the characteristics of light weight, slim thickness, low electric power consumption, the liquid crystal display device (or, LCD) is being widely applied. Concomitant with this wide application, the LCD is used for office automation devices and audio/video devices. The LCD displays a picture data (or an image) by using the physical property of crystal that changes array in response to voltage or temperature. That is, in general, the liquid crystal display device (LCD) displays a picture by making each of liquid crystal cells in a matrix of liquid crystal cells at a liquid crystal display panel to control light transmissivity according to a video signal.
As the LCD is not a self-luminescent element, the LCD requires, at a rear surface of the liquid crystal display panel, a backlight unit for irradiating light to the liquid crystal display panel for displaying an image. That is, liquid crystal display (LCD) panels, which are mounted to display devices or the like, do not have a self-luminous function. For this reason, a backlight unit (BLU) is disposed at the rear of such an LCD panel, to generate light and to provide the generated light to the LCD panel.
Generally, an LCD includes an array substrate, a color filter substrate, a layer of liquid crystal panel provided between the array substrate and the color filter substrate, and a backlight unit emitting light to the liquid crystal panel.
There are two kinds of the backlight units for LCD, one is the direct type backlight unit and the other is the edge type backlight unit. The edge type backlight unit includes a light guide panel and light emitting diodes. The light emitting diodes are arranged at a lateral surface of the light guide panel. The light guide panel guides the light emitted from the light emitting diodes through a total reflection, and emits the light to the liquid crystal panel.
On the other hands, for the direct type backlight unit, no light guide panel is used and light emitting diodes are arranged at a rear surface of the light guide panel, whereby the light emitting diodes emit light toward the rear surface of the liquid crystal panel.
The backlight unit must uniformly emit light to the liquid crystal panel. That is, efforts are being waged to improve brightness uniformity of the liquid crystal display device.